Bandgap voltage references are one of the main building blocks used in electronic circuits. Bandgap voltage references may be used in a myriad of applications, including cell phones, MP3 players, personal digital assistants, cameras, video recorders, and others.
Simply stated, a bandgap voltage reference receives a power supply and generates an output voltage. The bandgap voltage reference may be designed to provide an output voltage that is stable over temperature, or it may be designed to provide an output voltage that varies over temperature, for example to compensate for a change caused by temperature in another circuit or circuit element.
The output of the reference voltage may be used for a number of purposes. For example, a reference voltage output that is stable over temperature, that is, has a low temperature coefficient, can be placed across an external resistor to generate a current that is stable over temperature. Also, a reference voltage output can be used along with a regulator circuit to provide a regulated power supply.
Conventional bandgap circuits provide output voltages on the order of the bandgap of silicon or higher, that is, they provide output voltages that are at or exceed approximately 1.26 volts, though this value depends on the specific processing technology used. However, many modern circuits require a voltage less than the bandgap of silicon. For example, many newer technologies provide devices that have excessive leakage when their drain voltages are higher than approximately 1 volt. Also, lower voltages are often used where it is particularly desirable to save power. Another drawback of conventional circuits is that their temperature characteristics cannot be adjusted without changing their output voltage.
Thus, what is needed are circuits, methods, and apparatus that provide bandgap voltage references having output voltages less than the bandgap of silicon. It is also desirable that the output voltage and temperature coefficient be independently adjustable.